Copolymers having a gradient structure

ABSTRACT

The present invention relates to a copolymer, especially for use as a dispersant for solid particles, in particular for use as dispersant for mineral binder compositions, having a polymer backbone and side chains bonded thereto, comprising at least one ionizable monomer unit M1 and at least one side chain-bearing monomer unit M2, wherein the copolymer has a gradient structure in at least one section A in a direction along the polymer backbone with regard to the ionizable monomer unit M1 and/or with regard to the side chain-bearing monomer unit M2.

TECHNICAL FIELD

The invention relates to a copolymer, especially for use as dispersant for solid particles, in particular for use as dispersant for mineral binder compositions, having a polymer backbone and side chains bonded thereto, comprising at least one ionizable monomer unit and at least one side chain-bearing monomer unit. The invention additionally relates to a process for preparing a copolymer, to the use of copolymers and to a mineral binder composition and to shaped bodies formed therefrom and comprising copolymers.

PRIOR ART

Dispersants or fluxes are used in the building industry as plasticizers or water-reducing agents for mineral binder compositions, for example concrete, mortar, cements, gypsums and lime. The dispersants are generally organic polymers which are added to the makeup water or admixed with the binder compositions in solid form. In this way, it is advantageously possible to alter both the consistency of the binder composition during processing and the properties in the hardened state.

Known particularly effective dispersants are, for example, comb polymers based on polycarboxylate. Comb polymers of this kind have a polymer backbone and side chains bonded thereto. Corresponding polymers are described, for example, in EP 1 138 697 A1 (Sika AG).

Likewise known as concrete additives are copolymer mixtures as mentioned, for example, in EP 1 110 981 A2 (Kao). The copolymer mixtures are prepared by converting ethylenically unsaturated monomers in a free-radical polymerization reaction, wherein the molar ratio of the two monomers is altered at least once during the polymerization process.

Comb polymers of this kind are very effective, but in some cases, according to the application, have to be used in relatively high dosages, which is disadvantageous from an economic point of view. According to the binder composition, the comb polymers additionally lose their effect after just a short time.

It is possible to at least partly compensate for these drawbacks of the comb polymers by combination with further admixtures. However, solutions of this kind are usually complicated in their application and costly.

There is therefore still a need for improved dispersants that do not have the disadvantages mentioned.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to overcome the aforementioned disadvantages. More particularly, an improved dispersant is to be provided, especially for solid particles and in particular for mineral binder compositions. The dispersant is in particular to enable effective plasticization and good working of mineral binder compositions. In particular, the effect of the dispersant is to be maintained over a maximum period of time. Moreover, what is desired is for the dispersant to be producible in a very flexible and controlled manner.

It has been found that, surprisingly, this object can be achieved by the features of independent claim 1.

The core of the invention is accordingly a copolymer, especially for use as a dispersant for solid particles, in particular for use as dispersant for mineral binder compositions, having a polymer backbone and side chains bonded thereto, comprising at least one ionizable monomer unit M1 and at least one side chain-bearing monomer unit M2, wherein the copolymer has a gradient structure in at least one section in a direction along the polymer backbone with regard to the ionizable monomer unit M1 and/or with regard to the side chain-bearing monomer unit M2.

As has been shown, copolymers of this kind, by comparison with known dispersants, firstly result in very good plasticizing effects in mineral binder compositions which are additionally maintained for a comparatively longer period. Compared to comparable polymers having purely statistical (=random) distribution of the monomer units or having a purely blockwise arrangement of the monomer units, significantly better plasticization performance can be observed in some cases. Moreover, the copolymers of the invention can be prepared in a reliable manner in a wide variety of different modifications in an efficient process. The copolymers of the invention can thus be produced very flexibly and in a controlled manner.

Further aspects of the invention are the subject of further independent claims. Particularly preferred embodiments of the invention are the subject of the dependent claims.

WAYS OF EXECUTING THE INVENTION

A first aspect of the present invention relates to a copolymer, especially for use as a dispersant for solid particles, in particular for use as dispersant for mineral binder compositions, having a polymer backbone and side chains bonded thereto, comprising at least one ionizable monomer unit M1 and at least one side chain-bearing monomer unit M2, wherein the copolymer has a gradient structure in at least one section A in a direction along the polymer backbone with regard to the ionizable monomer unit M1 and/or with regard to the side chain-bearing monomer unit M2.

In other words, in the copolymer of the invention, there is a concentration gradient in at least one section A in a direction along the polymer backbone with regard to the ionizable monomer unit M1 and/or with regard to the side chain-bearing monomer unit M2.

The term “gradient structure” or “concentration gradient” in the present case is especially a continuous change in the local concentration of a monomer unit in at least one section in a direction along the copolymer backbone. Another term for “concentration gradient” is “concentration slope”.

The concentration gradient may, for example, be essentially constant. This corresponds to a linear decrease or increase in the local concentration of the respective monomer unit in the at least one section A in the direction of the copolymer backbone. However, it is possible that the concentration gradient changes in the direction of the copolymer backbone. In this case, there is a nonlinear decrease or increase in the local concentration of the respective monomer unit. The concentration gradient extends especially over at least 10, especially at least 14, preferably at least 20 or at least 40, monomer units of the copolymer.

By contrast, abrupt or sharp changes in concentration of monomers as occur, for example, in the case of block copolymers are not referred to as a concentration gradient.

The expression “local concentration” in the present context refers to the concentration of a particular monomer at a given point in the polymer backbone. In practice, the local concentration or the mean of the local concentration can be ascertained, for example, by determining the monomer conversions during the preparation of the copolymer. In this case, the monomers converted within a particular period can be ascertained. The averaged local concentration especially corresponds to the ratio of the mole fraction of a particular monomer converted within the period of time in question to the total molar amount of the monomers converted within the period of time in question.

The conversions of the monomers can be determined in a manner known per se, for example, with the aid of liquid chromatography, especially high-performance liquid chromatography (HPLC), and taking account of the amounts of monomers used.

In particular, it is also possible to analyze and to determine the structure of the copolymers by nuclear spin resonance spectroscopy (NMR spectroscopy). By ¹³C and ¹H NMR spectroscopy in particular, it is possible in a manner known per se to determine the sequence of the monomer units in the copolymer on the basis of neighboring group effects in the copolymer and using statistical evaluations.

The copolymer may also have more than one section A having a gradient structure, especially two, three, four or even more sections A, which are arranged in succession, for example. If present, different gradient structures or concentration slopes may each be present in the different sections A.

The terms “ionizable monomers” and “ionizable monomer units” especially mean monomers or polymerized monomers that are in anionic or negatively charged form at a pH>10, especially at a pH>12. These are especially H donor groups or acid groups. The ionizable groups are more preferably acid groups, for example carboxylic acid, sulfonic acid, phosphoric acid and/or phosphonic acid groups. Preference is given to carboxylic acid groups. The acid groups may also take the form of anions in deprotonated form or of a salt with a counterion or cation.

Preferably, in the at least one section A, a local concentration of the at least one ionizable monomer unit M1 increases continuously along the polymer backbone, while a local concentration of the at least one side chain-bearing monomer unit M2 decreases continuously along the polymer backbone, or vice versa.

A local concentration of the ionizable monomer unit M1 at the first end of the at least one section A is especially lower than at the second end of the section A, while a local concentration of the side chain-bearing monomer unit M2 at the first end of the section A is greater than at the second end of the section A, or vice versa.

More particularly, in the case of a division of the at least one section A into 10 subsections of equal length, the averaged local concentration of the at least one ionizable monomer unit M1 in the respective subsections along the polymer backbone increases in at least 3, especially in at least 5 or 8, successive subsections, while the averaged local concentration of the at least one side chain-bearing monomer unit M2 in the respective subsections along the polymer backbone decreases in at least 3, especially in at least 5 or 8, successive subsections, or vice versa.

Specifically, an increase or decrease in the averaged local concentration of the at least one ionizable monomer unit M1 in the successive subsections is essentially constant, while, advantageously, a decrease or increase in the averaged local concentration of the at least one side chain-bearing monomer unit M2 in the successive subsections is essentially likewise constant.

A weight-average molecular weight M_(W) of the overall copolymer is especially in the range of 10,000-150,000 g/mol, advantageously 12,000-80,000 g/mol, especially 12,000-50,000 g/mol. In the present context, molecular weights such as the weight-average molecular weight M_(W) or the number-average molecular weight M_(n) are determined by gel permeation chromatography (GPC) with polyethylene glycol (PEG) as standard. This technique is known per se to the person skilled in the art.

In a preferred embodiment, the polydispersity (=weight-average molecular weight M_(W)/number-average molecular weight M_(n)) of the copolymer is <1.5. In particular, the polydispersity is in the range of 1.0-1.4, especially 1.1-1.3.

In an advantageous embodiment, the at least one section A having the gradient structure, based on a total length of the polymer backbone, has a length of at least 30%, especially at least 50%, preferably at least 75% or 90%.

Advantageously, the at least one section A, based on a total number of monomer units in the polymer backbone, has a proportion of at least 30%, especially at least 50%, preferably at least 75% or 90%, of monomer units.

In particular, the at least one section A, based on the weight-average molecular weight of the overall copolymer, has a proportion by weight of at least 30%, especially at least 50%, preferably at least 75% or 90%.

Thus, the section A with the concentration gradient or the gradient structure is of particular importance.

The at least one section A having the concentration gradient advantageously comprises at least 5, especially at least 7, preferably at least 10, monomer units M1 and/or at least 5, especially at least 7, preferably at least 10, monomer units M2.

The at least one section A having the concentration gradient advantageously comprises at least 5, especially at least 7, preferably at least 10, monomer units M1 and at least 5, especially at least 7, preferably at least 10, monomer units M2. The at least one section A having the concentration gradient advantageously comprises 5-70, especially 7-40, preferably 10-25, monomer units M1 and 5-70, especially 7-40, preferably 10-25, monomer units M2.

More particularly, the copolymer consists to an extent of at least 50 mol %, in particular at least 75 mol %, especially at least 90 mol % or 95 mol %, of ionizable monomer units M1 and side chain-bearing monomer units M2.

It is advantageous when at least 30 mol %, especially at least 50 mol %, preferably at least 75 mol %, in particular at least 90 mol % or at least 95 mol %, of the ionizable monomer units M1 are in the at least one section A having a gradient structure.

Likewise advantageously, at least 30 mol %, especially at least 50 mol %, preferably at least 75 mol %, in particular at least 90 mol % or at least 95 mol %, of the side chain-bearing monomer units M2 are in the at least one section having a gradient structure.

Especially preferably, the two latter aforementioned conditions apply simultaneously.

In another advantageous embodiment, the copolymer, in addition to the at least one section A having a gradient structure, has a further section B, wherein there is essentially a constant local concentration of the monomers and/or a statistical or random distribution of the monomers over the entire section B. Section B may consist, for example, of a single kind of monomers or of multiple different monomers in statistical distribution. In section B, however, there is especially no gradient structure and no concentration gradient along the polymer backbone.

The copolymer may also have more than one further section B, for example two, three, four or even more sections B, which may differ from one another from a chemical and/or structural point of view.

Preferably, the at least one section A directly adjoins the further section B.

It has been found that, surprisingly, copolymers of this kind are even more advantageous under some circumstances with regard to the plasticizing effect and the maintenance thereof over time.

More particularly, the further section B comprises ionizable monomer units M1 and/or side chain-bearing monomer units M2.

Based on all the monomer units present therein, the further section B, in one embodiment of the invention, for example, comprises advantageously at least 30 mol %, especially at least 50 mol %, preferably at least 75 mol %, in particular at least 90 mol % or at least 95 mol %, of ionizable monomer units M1. Any proportion of side chain-bearing monomer units M2 present in the further section B is particularly less than 25 mol %, especially less than 10 mol % or less than 5 mol %, based on all monomer units M1 in the further section. More particularly, there are no side chain-bearing monomer units M2 in the further section B.

In a further and particularly advantageous implementation of the invention, the further section B, based on all the monomer units present therein, comprises at least 30 mol %, especially at least 50 mol %, preferably at least 75 mol %, in particular at least 90 mol % or at least 95 mol %, of side chain-bearing monomer units M2. In this case, any proportion of ionizable monomer units M1 present in the further section B is in particular less than 25 mol %, especially less than 10 mol % or less than 5 mol %, based on all monomer units M2 in the further section B. More particularly, there are no ionizable monomer units M1 in the further section B.

It has been found to be appropriate when the further section B comprises a total of 5-70, especially 7-40, preferably 10-25, monomer units. These are especially monomer units M1 and/or M2, side chain-bearing monomer units M2.

A ratio of the number of monomer units in the at least one section A having gradient structure to the number of monomer units in the at least one further section B having the essentially constant local concentration is advantageously in the range of 99:1-1:99, especially 10:90-90:10, preferably 80:20-20:80, especially 70:30-30:70.

The side chain-bearing monomer unit M2 especially includes polyalkylene oxide side chains, especially polyethylene oxide and/or polypropylene oxide side chains.

The ionizable monomer unit M1 preferably includes acid groups, especially carboxylic acid, sulfonic acid, phosphoric acid and/or phosphonic acid groups.

An especially preferred copolymer is one in which the ionizable monomer unit M1 has a structure of the formula I

The side chain-bearing monomer unit M2 includes, in particular, a structure of the formula II

where

-   -   R¹, in each case independently, is —COOM, —SO₂—OM, —O—PO(OM)₂         and/or —PO(OM)₂,     -   R², R³, R⁵ and R⁶, in each case independently, are H or an alkyl         group having 1 to 5 carbon atoms,     -   R⁴ and R⁷, in each case independently, are H, —COOM or an alkyl         group having 1 to 5 carbon atoms,         or where R¹ forms a ring together with R⁴ to give —CO—O—CO—,     -   M, independently of one another, represents H⁺, an alkali metal         ion, an alkaline earth metal ion, a di- or trivalent metal ion,         an ammonium ion or an organic ammonium group;     -   m=0, 1 or 2,     -   p=0 or 1,     -   X, in each case independently, is —O— or —NH—,     -   R⁸ is a group of the formula -[AO]_(n)—R^(a)     -   where A=C₂- to C₄-alkylene, R^(a) is H, a C₁- to C₂₀-alkyl         group, -cycloalkyl group or -alkylaryl group,     -   and n=2-250, especially 10-200.

Advantageously, a molar ratio of the ionizable monomer units M1 to the side chain-bearing monomer units M2 in the copolymer is in the range of 0.5-6, especially 0.7-4, preferably 0.9-3.8, further preferably 1.0-3.7 or 2-3.5. This achieves an optimal dispersing effect in mineral binder compositions.

In particular, R¹=COOM, R²=H or CH₃, R³=R⁴=H. It is thus possible to prepare the copolymer on the basis of acrylic or methacrylic acid monomers, which is of interest from an economic point of view. Moreover, copolymers of this kind in the present context result in a particularly good dispersing effect.

Copolymers with R¹=COOM, R²=H, R³=H and R⁴=COOM may likewise be advantageous. Such copolymers can be prepared on the basis of maleic acid monomers.

The X group in the ionizable monomer unit M2, advantageously in at least 75 mol %, particularly in at least 90 mol %, especially in at least 95 mol % or at least 99 mol % of all monomer units M2, is

—O— (=oxygen atom).

Advantageously, R⁵=H or CH₃, R⁶=R⁷=H and X=—O—. It is possible to prepare copolymers of this kind, for example, proceeding from (meth)acrylic esters, vinyl ethers, (meth)allyl ethers or isoprenol ethers.

In a particularly advantageous embodiment, R² and R⁵ are each mixtures of 40-60 mol % of H and 40-60 mol % of —CH₃.

In a further advantageous embodiment, R¹=COOM, R²=H, R⁵=—CH₃ and R³=R⁴=R⁶=R⁷=H.

In another advantageous embodiment, R¹=COOM, R²=R⁵=H or —CH₃ and R³=R⁴=R⁶=R⁷=H.

Especially advantageous copolymers are those in which: R¹=COOM; R² and R⁵ are each independently H, —CH₃ or mixtures thereof; R³ and R⁶ are each independently H or —CH₃, preferably H; R⁴ and R⁷ are each independently H or —COOM, preferably H.

The R⁸ radical in the side chain-bearing monomer unit M2, based on all the R⁸ radicals in the copolymer, consists of a polyethylene oxide especially to an extent of at least 50 mol %, especially at least 75 mol %, preferably at least 95 mol % or at least 99 mol %. A proportion of ethylene oxide units based on all the alkylene oxide units in the copolymer is especially more than 75 mol %, especially more than 90 mol %, preferably more than 95 mol % and specifically 100 mol %.

More particularly, R⁸ has essentially no hydrophobic groups, especially no alkylene oxides having three or more carbon atoms. This especially means that a proportion of alkylene oxides having three or more carbon atoms based on all the alkylene oxides is less than 5 mol %, especially less than 2 mol %, preferably less than 1 mol % or less than 0.1 mol %. In particular, there are no alkylene oxides having three or more carbon atoms or the proportion thereof is 0 mol %.

R^(a) is advantageously H and/or a methyl group. Particularly advantageously, A=C₂-alkylene and R^(a) is H or a methyl group.

More particularly, the parameter n=10-150, especially n=15-100, preferably n=17-70, specifically n=19-45 or n=20-25. In particular, this achieves excellent dispersing effects within the preferred ranges specified.

It may further be advantageous when the copolymer comprises at least one further monomer unit MS which especially differs chemically from the monomer units M1 and M2. In particular, multiple different further monomer units MS may be present. In this way, it is possible to further modify the properties of the copolymer and to adjust them, for example, with regard to specific applications.

Particularly advantageously, the at least one further monomer unit MS is a monomer unit of the formula III:

where

-   -   R^(5′), R^(6′), R^(7′), m′ and p′ are as defined for R⁵, R⁶, R⁷,         m and p;         -   Y, in each case independently, is a chemical bond or         -   —O—;         -   Z, in each case independently, is a chemical bond, —O— or             —NH—;         -   R⁹, in each case independently, is an alkyl group,             cycloalkyl group, alkylaryl group, aryl group, hydroxyalkyl             group or an acetoxyalkyl group, each having 1-20 carbon             atoms.

Advantageous examples of further monomer units MS are those where m′=0, p′=0, Z and Y represent a chemical bond and R⁹ is an alkylaryl group having 6-10 carbon atoms.

Also suitable are especially further monomer units MS in which m′=0, p′=1, Y is —O—, Z represents a chemical bond and R⁹ is an alkyl group having 1-4 carbon atoms.

Further suitable are further monomer units MS where m′=0, p′=1, Y is a chemical bond, Z is —O— and R⁹ is an alkyl group and/or a hydroxyalkyl group having 1-6 carbon atoms.

Particularly advantageously, the at least one further monomer unit MS consists of polymerized vinyl acetate, styrene and/or hydroxyalkyl (meth)acrylate, especially hydroxyethyl acrylate.

The at least one further monomer unit MS may be part of the at least one section A and/or of the further section B. It is also possible that the at least one further monomer unit MS is part of an additional section of the copolymer. More particularly, different further monomer units MS may be present in the different sections.

If present in the at least one section A, the at least one further monomer unit MS advantageously has a proportion in the at least one section A of 0.001-80 mol %, preferably 20-75 mol %, especially 30-70 mol %, based on all the monomer units in the first section A.

If present in the further section B, the at least one further monomer unit MS especially has a proportion in the further section B of 0.001-80 mol %, preferably 20-75 mol %, especially 30-70 mol % or 50-70 mol %, based on all the monomer units in the further section B.

In an advantageous embodiment, the at least one further monomer unit MS is present in the at least one section A and/or in the further section B with a proportion of 20-75 mol %, especially 30-70 mol %, based on all monomer units in the respective section.

In an advantageous embodiment, the copolymer consists of the at least one section A. In another advantageous embodiment, the copolymer consists of the at least one section A and the further section B. The latter case in particular results in very good and long-lasting plasticizing effects.

However, it is also possible, for example, that the copolymer contains at least two different sections A and/or at least two different further sections B.

A particularly advantageous copolymer has at least one or more than one of the following features:

-   (i) The copolymer consists to an extent of at least 75 mol %,     especially at least 90 mol % or 95 mol %, of ionizable monomer units     M1 and side chain-bearing monomer units M2; -   (ii) The copolymer comprises or consists of at least one section A     and a further section B; -   (iii) The further section B comprises side chain-bearing monomer     units M2, especially at least 50 mol %, preferably at least 75 mol     %, in particular at least 90 mol % or at least 95 mol %, based on     all the monomer units present in the section B. Any proportion of     ionizable monomer units M1 present in the further section B is less     than 25 mol %, especially less than 10 mol % or less than 5 mol %,     based on all monomer units M2 in the further section B. -   (iv) A molar ratio of the monomer units M1 to the monomer units M2     in the copolymer is in the range of 0.5-6, preferably 0.8-3.5; -   (v) R¹ is COOM; -   (vi) R² and R⁵ are H or CH₃, preferably CH₃; -   (vii) R³=R⁴=R⁶=R⁷=H; -   (viii) m=0 and p=1; -   (ix) X=—O— -   (x) A=C₂-alkylene and n=10-150, preferably 15-50; -   (xi) R^(a)=H or —CH₃, preferably CH₃.

An especially preferred copolymer is one consisting of sections A and B which has at least all the features (i)-(iv). Further preferred is a copolymer having all the features (i)-(xi). Even further preferred is a copolymer which fulfills all the features (i)-(xi) in the executions preferred in each case.

The copolymer is particularly a polymer having essentially linear structure. This particularly means that all monomer units of the copolymer are arranged in a single and/or unbranched polymer chain. Specifically, the copolymer does not have a star-shaped structure and/or the copolymer is not part of a branched polymer. More particularly, the copolymer is not part of a polymer in which there are multiple, especially three or more, polymer chains running in different directions attached to a central molecule.

The copolymer may be in liquid or solid form. More preferably, the copolymer is present as a constituent of a solution or dispersion, wherein a proportion of the copolymer is especially 10-90% by weight, preferably 25-65% by weight. This means that the copolymer can be added, for example, very efficiently to binder compositions.

In accordance with another advantageous embodiment, the copolymer is in the solid state of matter, especially in the form of a powder, in the form of pellets and/or sheets. This especially simplifies the transport of the copolymers. Solutions or dispersions of the copolymers can be converted to the solid state of matter, for example, by spray-drying.

A further aspect of the present invention relates to a process for preparing a copolymer, especially a copolymer as described above, wherein ionizable monomers m1 and side chain-bearing monomers m2 are polymerized together to form a concentration gradient and/or a gradient structure.

The ionizable monomers m1, on completion of polymerization, correspond to the abovementioned ionizable monomer units M1 of the copolymer. The side chain-bearing monomers m2, on completion of polymerization, likewise correspond to the above-described side chain-bearing monomer units M2.

More particularly, during the polymerization, a molar ratio of free ionizable monomers m1 to free side chain-bearing monomers m2 is at least temporarily altered. Specifically, the alteration of the molar ratio includes a continuous alteration. It is thus possible to form, in an efficiently controllable manner, a concentration gradient or a gradient structure.

Optionally, in addition, there is a stepwise change in the molar ratio of the free ionizable monomers m1 to the free side chain-bearing monomers m2. Especially prior to conduction of the continuous alteration. In this way, for example, a copolymer having a further section B is obtainable.

In a preferred embodiment, in a first step a), a portion of the ionizable monomers m1 is converted or polymerized essentially in the absence of side chain-bearing monomers m2 and, after attainment of a predetermined conversion, in a second step b), the as yet unconverted ionizable monomers m1 are polymerized together with the side chain-bearing monomers m2. In this way, in a simple and inexpensive manner, a copolymer having a further section B consisting essentially of polymerized ionizable monomers m1 is preparable.

Likewise advantageously, in a first step a), a portion of the side chain-bearing monomers m2 can be converted or polymerized essentially in the absence of ionizable monomers m1 and, after attainment of a predetermined conversion, in a second step b), the as yet unconverted side chain-bearing monomers m2 can be polymerized together with the ionizable monomers m1. This variant is particularly preferred. In this way, in a simple and inexpensive manner, a copolymer having a further section B consisting essentially of polymerized side chain-bearing monomers m2 is obtainable.

It is advantageous here to conduct steps a) and b) in immediate succession. In this way, it is possible to maintain the polymerization reaction in steps a) and b) to the best possible degree.

The polymerization in step a) is especially conducted until 0.1-85 mol %, especially 1-74 mol %, preferably 10-70 mol %, in particular 25-70 mol %, especially 28-50 mol % or 30-50 mol %, of the ionizable monomers m1 or of the side chain-bearing monomers m2 have been converted or polymerized. A conversion of 40-45 mol % is particularly advantageous.

The conversion of the monomers m1 and m2 or the progress of the polymerization can be monitored in a manner known per se, for example, with the aid of liquid chromatography, especially high-performance liquid chromatography (HPLC).

More particularly, the ionizable monomers m1 have a structure of the formula IV:

and the side chain-bearing monomers m2 have a structure of the formula V:

where R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, m, p and X are defined as described above.

In a further advantageous embodiment, during the polymerization or during step a) and/or during step b), at least one further polymerizable monomer ms is present, which is especially a monomer of the formula VI:

where R^(5′), R^(6′), R^(7′), R⁹ m′, p′, Y and Z are as defined above.

The further monomer ms, on completion of polymerization, corresponds to the above-described further monomer unit MS.

Particularly advantageously, the at least one further monomer ms is selected from vinyl acetate, styrene, N-vinylpyrrolidone and/or hydroxyalkyl (meth)acrylate, especially hydroxyalkyl acrylate.

The process can be conducted, for example, by, in step a), initially charging monomers m2 in a solvent, for example water, and then polymerizing them to give a further section B. As soon as the desired conversion of monomer m2 has been attained (e.g. 30-45 mol %; see above), without a time delay, in step b), monomers m1 are added and the polymerization is continued. The monomers m1 and the as yet unconverted monomers m2 are joined on here to the section B already formed, which forms a section A having a gradient structure. The polymerization is advantageously again continued until the desired conversion of monomer m1 (e.g. 75-95 mol %, especially 80-92 mol %; see above) has been attained. This affords, for example, a copolymer comprising a section A joined to a further section B.

In a further advantageous embodiment, in step a) and/or in step b), there is at least one further polymerizable monomer ms as described above. The at least one further polymerizable monomer ms in this case is especially polymerized together with the monomer m1 and/or the monomer m2.

Alternatively, it is possible, in addition to step a) and step b), to provide a further step c) for polymerization of the at least one further polymerizable monomer ms. In this way, it is possible to prepare a copolymer having an additional section C. More particularly, step c) can be conducted between step a) and step b) in time. Thus, the additional section C is arranged between sections A and B in space.

Alternatively, it is possible to conduct step c) before or after steps a) and b). Thus, the additional section C may be arranged after section A or before section B.

The polymerization is advantageously effected by a controlled free-radical polymerization and/or by a living free-radical polymerization. Particular preference is given to a reversible addition-fragmentation chain transfer polymerization (RAFT). A free-radical polymerization can basically be divided into three steps: initiation, growth and termination.

“Living free-radical polymerization” is also referred to as “controlled free-radical polymerization” and is known per se to the person skilled in the art in other contexts. The term comprehends chain growth processes in which essentially no chain termination reactions (transfer and termination) take place. Living free-radical polymerization thus proceeds essentially in the absence of irreversible transfer or termination reactions. These criteria can be fulfilled, for example, when the polymerization initiator is already used up at a very early stage during the polymerization and there is exchange between the species of different reactivity that proceeds at least as rapidly as the chain propagation itself. The number of active chain ends especially remains essentially constant during the polymerization. This enables essentially simultaneous growth of the chains that continues over the entire polymerization process. This correspondingly results in a narrow molecular weight distribution or polydispersity.

In other words, controlled free-radical polymerization or living free-radical polymerization is particularly notable for reversible or even absent termination or transfer reactions. After the initiation, the active sites are accordingly conserved over the entire reaction. All polymer chains are formed (initiated) simultaneously and grow continuously over the entire time. The free-radical functionality of the active site is ideally still conserved even after complete conversion of the monomers to be polymerized. This exceptional property of the controlled polymerizations enables preparation of well-defined structures such as gradient or block copolymers through sequential addition of different monomers.

By contrast, in conventional free-radical polymerization as described, for example, in EP 1 110 981 A2 (Kao), all three steps (initiation, growth and termination) proceed in parallel. The lifetime of each of the active, growing chains is very short and the monomer concentration during the chain growth of a chain remains essentially constant. The polymer chains thus formed do not have any active sites suitable for an addition of further monomers. Thus, this mechanism does not permit any control over the structure of the polymers. The preparation of gradient or block structures by means of conventional free-radical polymerization is therefore typically not possible (see, for example, “Polymere: Synthese, Synthese and Eigenschaften” [Polymers: Synthesis, Synthesis and Properties]; authors: Koltzenburg, Maskos, Nuyken; publisher: Springer Spektrum; ISBN: 97-3-642-34772-6 and “Fundamentals of Controlled/living Radical Polymerization”; publisher: Royal Society of Chemistry; editors: Tsarevsky, Sumerlin; ISBN: 978-1-84973-425-7).

Thus, there is a clear distinction of “living free-radical polymerization” from conventional “free-radical polymerization” or free polymerization conducted in a non-living or non-controlled manner.

In reversible addition-fragmentation chain transfer polymerization (RAFT), control over the polymerization is achieved by a reversible chain transfer reaction. Specifically, a growing free-radical chain adds on what is called a RAFT agent, which leads to formation of an intermediate free radical. The RAFT agent then fragments, in such a way as to reform another RAFT agent and a free radical available for propagation. In this way, the probability of propagation is distributed uniformly over all chains. The average chain length of the polymer formed is proportional to the RAFT agent concentration and to the reaction conversion. RAFT agents used are especially organic sulfur compounds. Particularly suitable are dithioesters, dithiocarbamates, trithiocarbonates and/or xanthates. The polymerization can be initiated in a conventional manner by means of initiators or thermal self-initiation.

Preferably, the polymerization or steps a) and/or b) are effected in an aqueous solution. More particularly, the polymerizations in both steps a) and b) are effected in aqueous solutions. This is also correspondingly true of step c) if it is conducted. As has been found, this has a positive effect on the dispersing action of the copolymer.

Alternatively, it is possible to provide other solvents, for example ethanol.

The initiator used for the polymerization is especially a free-radical initiator, preferably an azo compound and/or a peroxide. Suitable peroxides are selected, for example, from the group consisting of dibenzoyl peroxide (DBPO), di-tert-butyl peroxide and diacetyl peroxide.

A particularly advantageous initiator is an azo compound, for example azobisisobutyronitrile (AIBN), α, α′-azodiisobutyram idine dihydrochloride (AAPH) or azobisisobutyramidine (AIBA). Other free-radical initiators, e.g. sodium persulfate or di-tert-butyl hyponitrite, can alternatively be used under some circumstances.

If the polymerization is effected in an aqueous solution or in water, α,α′-azodiisobutyramidine dihydrochloride (AAPH) is advantageously used as initiator.

Preferably, during the polymerization or in steps a) and/or b), one or more representatives from the group consisting of dithioesters, dithiocarbamates, trithiocarbonates and xanthates is present. These are called “RAFT agents”, and enable control over the polymerization process. This is also correspondingly true of step c) if it is conducted.

More particularly, the polymerization, or step a), step b) and/or step c), is effected at a temperature in the range of 50-95° C., especially 70-90° C.

It is advantageous to work under inert gas atmosphere, for example under nitrogen atmosphere.

A further aspect of the present invention comprises a copolymer obtainable by the process described above.

The present invention further relates to the use of a copolymer as described above as dispersant for solid particles.

The term “solid particles” means particles composed of inorganic and/or organic materials. In particular, these are inorganic and/or mineral particles.

Particularly advantageously, the copolymer is used as dispersant for mineral binder compositions. The copolymer can especially be used for plasticization, for water reduction and/or for improvement of the workability of a mineral binder composition.

More particularly, the copolymer can be used for extending the workability of a mineral binder composition.

The present invention further additionally relates to a mineral binder composition comprising at least one copolymer as described above.

The mineral binder composition comprises at least one mineral binder. The expression “mineral binder” is especially understood to mean a binder which reacts in the presence of water in a hydration reaction to give solid hydrates or hydrate phases. This may, for example, be a hydraulic binder (e.g. cement or hydraulic lime), a latently hydraulic binder (e.g. slag), a pozzolanic binder (e.g. fly ash) or a nonhydraulic binder (gypsum or white lime).

More particularly, the mineral binder or the binder composition comprises a hydraulic binder, preferably cement. Particular preference is given to a cement having a cement clinker content of ≥35% by weight. More particularly, the cement is of the CEM I, CEM II, CEM III, CEM IV or CEM V type (according to standard EN 197-1). A proportion of the hydraulic binder in the overall mineral binder is advantageously at least 5% by weight, especially at least 20% by weight, preferably at least 35% by weight, especially at least 65% by weight. In a further advantageous embodiment, the mineral binder consists to an extent of ≥95% by weight of hydraulic binder, especially of cement or cement clinker.

Alternatively, it may be advantageous when the mineral binder or the mineral binder composition comprises or consists of other binders. These are especially latently hydraulic binders and/or pozzolanic binders. Suitable latently hydraulic and/or pozzolanic binders are, for example, slag, fly ash and/or silica dust. The binder composition may likewise comprise inert substances, for example limestone, quartz flours and/or pigments. In an advantageous embodiment, the mineral binder contains 5-95% by weight, especially 5-65% by weight, more preferably 15-35% by weight, of latently hydraulic and/or pozzolanic binders. Advantageous latently hydraulic and/or pozzolanic binders are slag and/or fly ash.

In a particularly preferred embodiment, the mineral binder comprises a hydraulic binder, especially cement or cement clinker, and a latently hydraulic and/or pozzolanic binder, preferably slag and/or fly ash. The proportion of the latently hydraulic and/or pozzolanic binder in this case is more preferably 5-65% by weight, more preferably 15-35% by weight, while at least 35% by weight, especially at least 65% by weight, of the hydraulic binder is present.

The mineral binder composition is preferably a mortar or concrete composition.

The mineral binder composition is especially a workable mineral binder composition and/or one which is made up with water.

A weight ratio of water to binder in the mineral binder composition is preferably in the range of 0.25-0.7, particularly 0.26-0.65, preferably 0.27-0.60, especially 0.28-0.55.

The copolymer is advantageously used with a proportion of 0.01-10% by weight, especially 0.1-7% by weight or 0.2-5% by weight, based on the binder content. The proportion of the copolymer is based on the copolymer per se. In the case of a copolymer in the form of a solution, it is the solids content that is correspondingly crucial.

An additional aspect of the present invention relates to a shaped body, especially a constituent of a built structure, obtainable by curing a mineral binder composition comprising a copolymer as described above after addition of water. A built structure may, for example, be a bridge, a building, a tunnel, a roadway or a runway.

Further advantageous embodiments of the invention will be apparent from the working examples which follow.

BRIEF DESCRIPTION OF THE DRAWING

The figures used to elucidate the working examples show:

FIG. 1: The plot of the monomer conversions against time in the preparation of a copolymer of the invention (P1);

FIG. 2: A schematic diagram of a possible structure of a copolymer which can be derived from the conversions according to FIG. 1.

WORKING EXAMPLES

1. Preparation Examples for Polymers

1.1 Reference Polymer R1 (Comparative Example, Block Copolymer)

For preparation of a block copolymer by means of RAFT polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and a gas inlet tube is initially charged with 57.4 g of 50% methoxy polyethylene glycol 1000 methacrylate (0.03 mol) and 22 g of deionized water. The reaction mixture is heated to 80° C. with vigorous stirring. A gentle N2 inert gas stream is passed through the solution during the heating and over all the remaining reaction time. 378 mg of 4-cyano-4-(thiobenzoyl)pentanoic acid (1.35 mmol) are then added to the mixture. Once the substance has fully dissolved, 67 mg of AIBN (0.41 mmol) are added. From then on, the conversion is determined regularly by means of HPLC.

As soon as the conversion, based on methoxy polyethylene glycol methacrylate, is 90 mol %, 4.66 g of methacrylic acid (0.05 mol) are added. The mixture left to react for a further 4 h and then to cool. What remains is a clear, reddish, aqueous solution having a solids content of around 40%.

The copolymer thus obtained is referred to as reference polymer R1 and, owing to the virtually complete conversion of the methoxy polyethylene glycol methacrylate (90 mol %), has a block structure in which the side chain-bearing monomer units (methoxy polyethylene glycol methacrylate) are present in a first block and the ionizable monomer units (methacrylic acid) essentially spatially separately in a second block.

1.2 Reference Polymer R2 (Comparative Example, Statistical Polymer)

A reaction vessel is initially charged with 1.4 g of sodium hypophosphite and 36 g of deionized water. The reaction solution is heated to 80° C. To this solution is added dropwise, within 120 min, a mixture of 108.3 g of 50% methoxy polyethylene glycol-1000 methacrylate, 8.6 g of methacrylic acid and 20 g of water. At the same time, within 130 min, a solution of 0.89 g of sodium persulfate and 20 g of water is added dropwise. After this has ended, the solution is cooled down. What remains is a pale yellowish, slightly viscous polymer.

The copolymer thus obtained is referred to as reference polymer R2 and has a statistical or random distribution of the monomer units (methoxy polyethylene glycol methacrylate units and methacrylic acid units).

1.3 Copolymer P1

For preparation of the gradient polymer by means of RAFT polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and a gas inlet tube is initially charged with 57.4 g of 50% methoxy polyethylene glycol-1000 methacrylate (0.03 mol) and 22 g of deionized water. The reaction mixture is heated to 80° C. with vigorous stirring. A gentle N2 inert gas stream is passed through the solution during the heating and over all the remaining reaction time. 378 mg of 4-cyano-4-(thiobenzoyl)pentanoic acid (1.35 mmol) are then added to the mixture. Once the substance has fully dissolved, 67 mg of AIBN (0.41 mmol) are added. From then on, the conversion is determined regularly by means of HPLC.

As soon as the conversion, based on methoxy polyethylene glycol methacrylate, is 65 mol %, 4.66 g of methacrylic acid (0.05 mol) dissolved in 20 g of H₂O are added dropwise within 20 min. After this has ended, the mixture is left to react for a further 4 h and then to cool. What remains is a clear, pale reddish, aqueous solution having a solids content of around 35%. The copolymer with gradient structure thus obtained is referred to as copolymer P1.

FIG. 1 shows the plot of the monomer conversions against time in the preparation of the copolymer P1. The monomer conversions were determined in a manner known per se at the times given in FIG. 1 during the preparation of the copolymer by high-performance liquid chromatography (HPLC). The upper dotted curve which begins at the origin at time t=0 minutes represents the percentage conversion of the methoxy polyethylene glycol methacrylate monomers (=side chain-bearing monomers m2) (scale to the right). The lower dotted curve which begins at time t=25 minutes represents the percentage conversion of the methacrylic acid monomers (=ionizable monomers m1) (scale to the right). The solid line with the diamond-shaped points indicates the number of side chain-bearing monomers m2 which have been polymerized since the preceding measurement point (=n(M2); left-hand scale). Correspondingly, the solid line with the triangular points indicates the number of ionizable monomers m1 which have been polymerized since the preceding measurement point (=n(M1); left-hand scale).

Using the data in FIG. 1 for the period from 0 to 55 minutes at the particular time to calculate the ratio n(M2)/[n(M1)+n(M2)] and n(M1)/[n(M1)+n(M2)], the following values are found:

TABLE 1 Monomer ratios during the preparation of the copolymer P1. Time n(M2)/[n(M1) + n(M2)] n(M1)/[n(M1) + n(M2)] 15 100%   0% 25 100%   0% 30 33% 67% 35 29% 71% 40 25% 75% 45 17% 83% 55 10% 90%

It is apparent from table 1 that, in the preparation of the copolymer P1, during the first 25 minutes, a section consisting of 100% side chain-bearing monomer units M2 is formed, followed by a section in which the proportion of side chain-bearing monomer units M2 decreases continuously while the proportion of ionizable monomer units M1 increases continuously.

FIG. 2 additionally shows a schematic of a possible structure of the copolymer P1. This can be inferred directly from the conversions shown in FIG. 1. The side chain-bearing monomer units M2 (=polymerized methoxy polyethylene glycol methacrylate monomers) are represented as a circle with a twisted appendage. The ionizable monomer units M1 are represented as dumbbell-shaped symbols.

It is apparent from FIG. 2 that copolymer P1 comprises a first section A with gradient structure and a further section B consisting essentially of side chain-bearing monomer units.

1.4 Copolymer P2

For preparation of the gradient polymer by means of RAFT polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and a gas inlet tube is initially charged with 57.4 g of 50% methoxy polyethylene glycol-1000 methacrylate (0.03 mol) and 22 g of deionized water. The reaction mixture is heated to 80° C. with vigorous stirring. A gentle N2 inert gas stream is passed through the solution during the heating and over all the remaining reaction time. 378 mg of 4-cyano-4-(thiobenzoyl)pentanoic acid (1.35 mmol) are then added to the mixture. Once the substance has fully dissolved, 67 mg of AIBN (0.41 mmol) are added. From then on, the conversion is determined regularly by means of HPLC.

As soon as the conversion, based on methoxy polyethylene glycol methacrylate, is 45 mol %, 4.66 g of methacrylic acid (0.05 mol) dissolved in 20 g of H₂O are added dropwise within 20 min. After this has ended, the mixture is left to react for a further 4 h and then to cool. What remains is a clear, pale reddish, aqueous solution having a solids content of around 35%. The copolymer with gradient structure thus obtained is referred to as copolymer P2.

1.5 Copolymer P3

For preparation of the gradient polymer by means of RAFT polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and a gas inlet tube is initially charged with 57.4 g of 50% methoxy polyethylene glycol-1000 methacrylate (0.03 mol) and 22 g of deionized water. The reaction mixture is heated to 80° C. with vigorous stirring. A gentle N2 inert gas stream is passed through the solution during the heating and over all the remaining reaction time. 378 mg of 4-cyano-4-(thiobenzoyl)pentanoic acid (1.35 mmol) are then added to the mixture. Once the substance has fully dissolved, 67 mg of AIBN (0.41 mmol) are added. From then on, the conversion is determined regularly by means of HPLC.

As soon as the conversion, based on methoxy polyethylene glycol methacrylate, is 30 mol %, 4.66 g of methacrylic acid (0.05 mol) dissolved in 20 g of H₂O are added dropwise within 20 min. After this has ended, the mixture is left to react for a further 4 h and then to cool. What remains is a clear, pale reddish, aqueous solution having a solids content of around 35%. The copolymer with gradient structure thus obtained is referred to as copolymer P3.

2. Mortar Mixtures

2.1 Production

The mortar mixture used for test purposes has the dry composition described in table 2:

TABLE 2 Dry composition of mortar mixture Component Amount [g] Cement (CEM I 42.5 N; Normo 4; 750 g available from Holcim Schweiz) Limestone filler 141 g Sand 0-1 mm 738 g Sand 1-4 mm 1107 g  Sand 4-8 mm 1154 g 

To make up a mortar mixture, the sands, the limestone filler and the cement were dry-mixed in a Hobart mixer for 1 minute. Within 30 seconds, the makeup water (ratio of water to cement w/c=0.49), into which the respective polymer (proportion: 0.24% by weight; based on solids content of the polymer and based on cement content) had been admixed beforehand, was added and the mixture was mixed for a further 2.5 minutes. The total wet mixing time was 3 minutes in each case.

2.2 Mortar Tests

To determine the dispersancy of the polymers, the slump (ABM) of a series of made-up mortar mixtures was measured at different times. The slump (ABM) of the mortar was determined in accordance with EN 1015-3.

2.3 Results of the Mortar Tests

Table 3 gives an overview of the mortar tests conducted and the results achieved. Experiment V1 is a blank experiment conducted for comparative purposes without addition of a polymer.

TABLE 3 Results of mortar tests ABM^(#) [mm] after No. Polymer 0 min 30 min 60 min 90 min 120 min 150 min 180 min V1 — <120 n.m. n.m. n.m. n.m. n.m. n.m. V2 R1 240 184 163 140 127 n.m. n.m. V3 R2 208 194 171 160 148 135 n.m. E1 P1 192 165 162 161 150 152 147 E2 P2 244 225 219 209 205 187 180 E3 P3 230 217 229 219 199 166 138 n.m. = not measurable ^(#)= slump according to EN 1015-3. The time “0 min” corresponds to the first measurement immediately after the making-up of the mortar sample.

A comparison of the experiments shows that all copolymers P1-P3 having gradient structure have good and long-lasting plasticizing action. This is especially true of copolymer P2. By comparison, copolymers R1 and R2, which respectively have a pure block structure and a statistical monomer distribution, give distinctly poorer results.

It can thus be concluded from the results presented that the copolymers of the invention are advantageous over known polymers in various respects. More particularly, with the polymers of the invention, high dispersancies and plasticizations can be achieved, and these can also be maintained at a level of practical interest over a comparatively long period.

However, the above-described embodiments should be regarded merely as illustrative examples which can be modified as desired within the scope of the invention. 

The invention claimed is:
 1. A process for preparing a copolymer, the process comprising: polymerizing together ionizable monomers m1 and side chain-bearing monomers m2 to form a gradient structure in the copolymer, wherein the polymerization includes: converting or polymerizing a portion of the side chain-bearing monomers m2 to form at least one side chain-bearing monomer unit M2 essentially in the absence of the ionizable monomers m1 until a predetermined conversion is attained, the predetermined conversion being in a range of from 1 to 74 mol % of the side chain-bearing monomers m2 being converted or polymerized, and then polymerizing together unconverted side chain-bearing monomers m2 with the ionizable monomers m1, wherein: the copolymer has a polymer backbone and side chains bonded thereto, the copolymer comprises at least one ionizable monomer unit M1 and the at least one side chain-bearing monomer unit M2, and the copolymer has the gradient structure in at least one section A in a direction along the polymer backbone with regard to the ionizable monomer unit M1 and/or with regard to the side chain-bearing monomer unit M2.
 2. The process as claimed in claim 1, wherein a polydispersity of the copolymer is <1.5.
 3. The process as claimed in claim 1, wherein the at least one section A having the gradient structure has a proportion of at least 30% of monomer units, based on a total number of the monomer units in the polymer backbone.
 4. The process as claimed in claim 1, wherein the copolymer, in addition to the at least one section A, has a further section B having an essentially constant local concentration of monomers and/or a random distribution of monomers, and the further section B comprises the ionizable monomer units M1 and/or the side chain-bearing monomer units M2.
 5. The process as claimed in claim 4, wherein the further section B, based on all monomer units present therein, comprises at least 30 mol % of the side chain-bearing monomer units M2, and a proportion of the ionizable monomer units M1 present in the further section B is less than 25 mol %, based on all the monomer units M2 in the further section B.
 6. The process as claimed in claim 1, wherein the ionizable monomer unit M1 has a structure represented by formula I

and the side chain-bearing monomer unit M2 includes a structure represented by formula II

where: R¹, in each case independently, is —COOM, —SO₂—OM, —O—PO(OM)₂, or —PO(OM)₂, R², R³, R⁵ and R⁶, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms, R⁴ and R⁷, in each case independently, are H, —COOM, or an alkyl group having 1 to 5 carbon atoms, or where R¹ forms a ring together with R⁴ to give —CO—O—CO—, M, independently of one another, represents H⁺, an alkali metal ion, an alkaline earth metal ion, a di- or trivalent metal ion, an ammonium ion, or an organic ammonium group; m=0, 1, or 2, p=0 or 1, X, in each case independently, is —O— or —NH—, R⁸ is a group represented by formula -[AO]_(n)—R^(a) where A=C₂- to C₄-alkylene, R^(a) is H, a C₁- to C₂₀-alkyl group, -cycloalkyl group or -alkylaryl group, and n=2-250.
 7. The process as claimed in claim 1, wherein R¹=COOM; R² and R⁵, independently of one another, are H, —CH₃, or mixtures thereof; R³ and R⁶, independently of one another, are H or —CH₃; R⁴ and R⁷, independently of one another, are H or —COOM; and X in at least 75 mol % of all the monomer units M2 is —O—.
 8. The process as claimed in claim 1, wherein the polymerization of the ionizable monomers m1 and the side chain-bearing monomers m2 to form the gradient structure in the copolymer is effected by a controlled free-radical polymerization and/or a living free-radical polymerization.
 9. The process as claimed in claim 1, wherein the ionizable monomers m1 have a structure represented by formula IV:

and the side chain-bearing monomers m2 have a structure represented by formula V:

where R¹=COOM; R² and R⁵, independently of one another, are H, —CH₃, or mixtures thereof; R³ and R⁶, independently of one another, are H or —CH₃; R⁴ and R⁷, independently of one another, are H or —COOM; m=0, 1, or 2; p=0 or 1; and X in at least 75 mol % of all the monomer units M2 is —O—. 